fix: stabilize core error handling

Remove production panic and unwrap paths from core modules.

Propagate bookmark encryption failures, harden file watcher and temp mapped file handling, and clean up dead code in shared utilities.

src/system/watcher.rs

@@ -27,6 +27,8 @@ pub enum FsWatcherError {
     PathNotWatched,
     #[error("unable to watch path, since it's already watched")]
     PathAlreadyWatched,
+    #[error("watcher event channel disconnected")]
+    Disconnected,
     #[error("unknown event: {0}")]
     UnknownEvent(&'static str),
     #[error("worker error: {0}")]
@@ -114,7 +116,7 @@ impl FsWatcher {
         let res = match self.receiver.recv_timeout(Duration::from_millis(1)) {
             Ok(res) => res,
             Err(RecvTimeoutError::Timeout) => return Ok(None),
-            Err(RecvTimeoutError::Disconnected) => panic!("File watcher died"),
+            Err(RecvTimeoutError::Disconnected) => return Err(FsWatcherError::Disconnected),
         };
 
         // convert event to FsChange